The present invention relates to an improved transmitter coil of a fuze setter and improved fuze setter circuitry for adaptively tuning the circuit for resonance and current difference circuitry for interpreting a fuze talkback message.
Inductive fuze setters are well known in the art. U.S. Pat. No. 5,343,795, entitled "Settable Electronic Fuzing System For Cannon Ammunition", issued Sep. 6, 1994 to General Electric Co. is directed to one such system. The entire contents of U.S. Pat. No. 5,343,795 are hereby incorporated by reference. Inductive fuze setters are used to transmit detonation data to a projectile warhead, such as time-of-flight or turns-to-burst data, as is well known in the art. Rapid-fire canons can have a fire rate ranging from 10 rounds per minute to 10 rounds per second or greater, and therefore it is very important to be able to quickly transmit data to a projectile as it is moving from a magazine to the cannon. Moreover, it is extremely important to verify that the projectile has correctly received the transmitted data.
NATO has a standard STANAG 4369 and the AOP-22 which govern the communications between a fuze setter and a fuze. This specifies a 100 KHz carrier signal which is pulse width modulated (PWM) for the forward message, which transmits the detonation data to the projectile and pulse code modulated (PCM) for the reverse or talkback message, in which the faze confirms the transmitted data.
As is well known in the art, the magnetic interface between the fuze setter and the fuze must allow energy transfer to "charge" the fuze circuit as well as be sensitive enough to detect and interpret the talkback signal transmitted by the fuze circuit with the power available from the "charge" portion of the communication from the fuze setter.
The prior art detected and interpreted the talkback message by detecting the phase change that occurs between the fuze setter circuit voltage and current during talkback, as the fuze is modulating the fuze coil impedance. However, this method suffers from the problem of a loss of signal when the LC circuit of the fuze setter is at resonance due to a null in the phase response. In order to work properly the system must be tuned a little off of resonance to be near the maximum power transfer of resonance, but to also be away from the null point. A small change in the inductive fuze setter parameters, such as a drift in capacitance values or inductance values caused by temperature variations can shift the operating point back to resonance, resulting in a null and loss of phase response, so that no talkback message can be interpreted.